What’s the hardest part of building a SaaS as a solo founder?

Hey everyone,

I’m curious about something.
For those of you who are building (or have tried to build) a SaaS as a founder or indie hacker:
What’s the hardest part for you?
Not necessarily the technical side. I’m interested in the whole process of actually getting a SaaS off the ground.
What part has personally slowed you down the most?
And if you could completely remove one painful part of building a SaaS, what would it be?

I’m especially interested in hearing about things you’ve actually experienced, rather than what you think would be difficult.

Thanks!