I thought 5% to 7% of equity is more than enough for an investor in a startup that has the potential to be the next Facebook, Amazon or Google?

I thought 5% to 7% of equity is more than enough for an investor in a startup that has the potential to be the next Facebook, Amazon or Google? Why am I seeing others say 8% to 15%? That seems extremely high! Peter Thiel invested $500,000 into Facebook for a 7% equity stake. I am presently working on Project X, which many are saying has serious potential to become the next Facebook and possibly more of excuted well. I will be seeking capital from an investor, but this is the first time I am seeing that high of a number to give away for an angel or other investor at this early stage. I have been told the platform costs are $750,000 to $1,000,000, but we have presently talking to other firms that can develop the systems, and possibly at lower costs.