In season 3 of The Flash, episode 22 - Infantino Street, H.R. Wells (one of the many H.R. Wells) discovers his purpose. With the a new team member Tracy Brand, Wells finds a partner to inspire, drink coffee, and... fall in love, which leads to the following conversation:

H.R. Wells: I have to tell you, I haven't always felt I belong completely.

Tracy Brand: What?

H.R. Wells: Yeah, lacking a clear sense of purpose sometimes. But then you arrived.

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And you here I understand my purpose. It's us. You and me. That meeting of the mind that we have, it's just so powerful...

Unfortunately for this version of Wells, things don't turn out so great. If you haven't watched season 3, stop reading now!

This Wells dies. But at least he inspired Brand for a few days, which was enough for Brand to create a weapon which could possibly stop the evil Savitar. The show goes one step further in regards to purpose. In the following episode, Finish Line, on Wells' tombstone is the following quote:

The two most important days in your life are the day you are born and the day you find out why. - Mark Twain

According to Quote Investigator, it appears that Mark Twain never actually stated this. But, does that really take anything away from it?