Inverse of fun
I came across an interesting take on entrepreneurship from Shaan Puri on the My First Million podcast, where he was talking about the different types of long-term entrepreneurship paths you can take. He broke it down into parallel entrepreneurship, where you're doing several startups at a time, serial entrepreneurship where you're doing different types of startups one after the other, and repeat entrepreneurship, where you're doing one startup for a long time or at least staying in the same industry.
He commented that doing lots of startups in parallel is probably the most fun, but also the least likely to succeed. While at the opposite end of the spectrum, repeat entrepreneurship is lower risk but also less fun. I think this is spot on and applies even more generally to startup culture.
There are lots of people out there who are chasing ideas because they think they will be fun. But fun attracts lots of competition and makes these ideas harder to execute. Also, once the novelty of a new idea wears off, you might be tempted to jump to the next fun thing and never see an idea through to it's full potential. While if you can dedicate years to something, especially if you already have a head-start with some skills applicable to the sector, you can grow almost any idea, good or bad, into something that is a sustainable business.
The hard part is to put your head down and do the work when it's not so fun.