What's one startup lesson you wish you'd learned sooner

As my launch date gets closer, I've been reflecting on how much of building a product has nothing to do with code.

A few lessons have surprised me:

• Building is usually easier than deciding what to build.

• Users don't always use a product the way you expect.

• Small improvements repeated consistently beat big bursts of effort.

• Progress often feels invisible until you look back months later.

The biggest surprise for me has been how often assumptions turn out to be wrong. Features I thought people would love weren't always the most valuable, while simple things ended up mattering far more than expected.

So I'm curious:

What's one startup, product, or business lesson you wish someone had told you at the beginning?

And if you could go back and give your earlier self one piece of advice, what would it be?