Vesting is crucial for several reasons. Firstly, it aligns the interests of employees and co-founders with the long-term success of the company. By tying equity to continued service, it discourages early departures and ensures that only those who contribute significantly benefit from the company's growth. Secondly, vesting protects the company from scenarios where an early employee or co-founder leaves with a substantial equity stake, which could be detrimental to future fundraising and strategic planning.