The blinds are now going up pretty fast in relation to the stack sizes. Going by Dan Harrington's "M" calculation, which is the stack divided by all blinds+antes, a player with half the chips at his table (300,000) now has an M of 30, which is plenty. However, if he's only got a quarter of the chips at the table (150,000) and his opponent(s) have the rest, he only has an M of 15, which means he's running out of options. Less than that, and he's heading toward an all-in or fold situation.