From the people buying an IPO a "very successful" one is one that was under-priced and goes on to produce outsized returns afterwards, this means the company owners sold below some "real value".

The most successful IPOs for the company are where it sells a bunch of stock at prices that then stay steady or even go down, they traded (potentially worthless) paper for real cash. I suspect the majority of IPOs are "successful" in the second way even though they're "sold" as being (a chance?) at the first way.