I think it is important to keep some kind of perspective about your work, not matter what that might be. And that includes writers, full time or part time. There is nothing noble about being willing to sacrifice everything for success. If you wish to die a martyr that is up to you. But placing your work above your friends, your spouse, your energy, your time is not only bad form, but it is usually wasted effort.
Consider this: the nature of writing being what it is, your competitors (that is, the “big sellers”) are more entrenched than you are. They have more resources, and can afford lots of help with their writing. So even if you work twice, or maybe three times, as hard as your competition it is unlikely that you will ever be able to top them.
And if you try, I think it it much more likely that you will become burnt out from exhaustion and frustration, unable to conjure up the inspiration that you need to write good fiction. Everybody understands working hard. But if you are devoting nights, weekends, holidays to writing while neglecting your personal relationships, that’s not going to work out for anybody.
Remember that the road to writing success is long and you are going to be on that grind for a long time. It does no good to wear yourself out at the beginning of the race. As “Ice Cube” said, “Life ain’t a track meet, it’s a marathon.”