Concept

Founder vesting

Founder vesting means the company can repurchase unvested shares at cost until they vest. Four years monthly with a one-year cliff is the market default. It protects co-founders and later investors if someone leaves early — and it is what investors expect on the cap table.

Where founders get this wrong

Skipping vesting between co-founders 'because we trust each other' and then fighting over a departure.
Assuming acceleration, cliffs, and repurchase price are boilerplate you can ignore until counsel asks.
Leaving unvested stock undocumented while raising — investors will force the cleanup mid-process.