Dia dhaoibh a chairde! Tá ráiteas agam le haitriúcháin do mo chara, agus tatú a bheidh ann. Is é an Béarla ná:

Be patient and tough; someday this pain will be useful to you.

M'iarracht fhéin ná:

Bí foighneach agus láidir, lá éigin bainfidh tú tairbhe as an phian seo.

I'm having trouble translating 'tough'; de Bhaldy gives crua, láidir and daingean, but I thought 'crua' had slightly negative connotations (makes me think of severity). I had thought 'daingean' meant 'deep' but looking on potafocal.com I'm wondering is 'daingean' in fact more suitable than 'láidir' which obviously makes us think of 'strong' before it does 'tough'?

I chose 'bain tairbhe as' because I thought it suited better than 'beidh an phian seo úsáideach / fóinteach duit'.

Cad a cheapann sibh? Go raibh maith agaibh roimh ré as aon cabhair.

You might like to consider righin "tough, tenacious".

Example usage: Bí righin is rachaidh leat. "Perservere and you will succeed."

I like your use of tairbhe.

So, perhaps:

Bí foighneach agus righin - lá éigin bainfidh tú tairbhe as an bpian seo.

But wait for other comments on the suitability of the vocabulary, punctuation, etc., and/or confirmation ...

(Edited to strike out agus)

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

tá tú á scríobh sin fá mar a bheadh "as an phian" mícheart

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

I love righin as a word, so onomatopoeic.

Ah, so I did.

I forgot to add: "as a phian" is correct if you are using Ulster Irish, otherwise "as a bpian" would be more usual.

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Ah, tá righin níos fearr ná láidir ar aon nós, GRMA a Bhreandáin. De Bhaldy had that as well, it confused me the way it was put in because it listed: tough (of person) crua, láidir, daingean, then the second entry said something about to harden, or tough meat or something, then no. 3 was '(of person)' again, listing righin and dígeanta, so I didn't know if that was in a different context or what! Sorry I probably haven't explained myself very well there, I don't have it with me at the moment, I should have just typed out the whole entry for ye.

So 'righin' is possibly the best option, but 'daingean' is also quite good, meaning steadfast solid, firm? My gaeilgeoir friend said it makes her think of an anchor, which is the right sort of idea for strong, immovable.
Dígeanta doesn't seem to fit at all, potafocal.com has it as zealous, die-hard?

Agus botún ba ea é sin de mo pháirt, as an bpian atá ag teastáil uaim! Is bean Chonnachtach mé agus is as Gaillimh é mo chara atá ag fáil an tatú, mar sin Gaeilge Chonnacht atá i gceist againn! Ach GRMA a Lughaidh.

I like "daingean".

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It is recommended that you always wait for three to agree on a translation.
I speak Connemara Irish, and my input will often reflect that.
I will do an mp3 file on request for short translations.
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Yeah, "steadfast" works too.

I just noticed the agus between the adjectives. Should it not be Bí foighneach daingean instead?

And now I am wanting to find some alliteration. How about:

Bí foighneach fódúil (fódúil is "well-grounded, solid, stable, firm, sensible"

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

I put the 'agus' in because there's an 'and' in the English, would you not put it in sa Ghaeilge?

Ha I'm a bit of a yoke for the alliteration meself a Bhreandáin, but I think righin and daingean both have a meaning that alludes to more than 'fódúil' does - but that's just a personal thing! And I'm looking for the English word to describe what I'm trying to say about righin and daingean but I can't think of it - you know what I mean, when a word has lots of connotations, things that you implicate with it? Associative meaning?

The alliteration is a personal choice but Irish has more of a preference for alliterative pairs than English.

As for the "agus", I don't think you _can_ normally have agus between two adjectives in Irish - and you wouldn't normally leave "and" out of the English. It's a basic difference between the two languages.

If you stick with daingean or righin, I think you need to have:

Bí foighneach daingean
or Bí foighneach agus bí daingean
or
Bí foighneach righin
or Bí foighneach agus bí righin

Await further comment on this ...

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).