Am I making a mistake by investing unpaid time with the hope of a big pay off later?

I have been out of school for two years.

I have been volunteering for the last year.

I just got rejected from yet another job opening, but I did land this amazing internship with an amazing organization, but it is yet another unpaid opportunity.

So currently, I volunteer with one nonprofit, and intern at two organizations. So its not like I am doing nothing. I am putting in a lot of work, and expect to put in a lot more with this new internship.

And I feel fortunate to have the support I have been getting, not many parents would be so patient. But I'm starting to feel a strong sense of doubt and fear creeping in.

I do all of this so that I can open doors later on - I do hope to pursue a pretty intensive, but well respected science communication certification program next year.

Will all this unpaid work I've been putting pay off eventually?

Is it foolish to put in all the work without knowing if all that work spent towards that dream career will pay off?