During the deal, self-rationalization starts to kick-in. The founders probably start believing some of the big-company synergy stories: complementary customer base, already scaled resources, complementary product in the portfolio. "Cross-sale alone will pay for the deal in X months/years." Sometimes they do work out! But all too often, the inertia of the larger business prevents realizing that dream. Yet if the founders weren't good at producing a reality distortion bubble, they quite likely wouldn't have made it to the M&A table in the first place. So such illusions shouldn't be surprising, especially if the price is high.