[iwasphone]

Investors arrive at an amount based on their estimate of the company's value and the share of equity they receive in return for their investment. If the founders then get commitments from additional investors, the company would have to attain a much larger value at exit time (i.e., IPO or purchase) for any of the investors to get a reasonable return. When done with consent it's called overcommitting. When done without consent, it's called fraud.

Disclaimer: IANAI