If you've done a lot of work already, someone you brought on now would, if they were reasonable, not expect to get the same amount of equity as you.

Beware, though, because empirically founders tend to overestimate the percentage of the value of the company represented by the work they've already done. Founders tend to overestimate past work and underestimate future work, and they also underestimate the distance between a good product and a successful company.