49.9k doesn't do it, but there's no way to be sure what level of assets will give you that 50k income. Having a dollar less is equivalent to having your target, plus an unexpected $1 rental expense. You are essentially choosing a level you are comfortable with that cannot be objective (probability that the extra $1 rental expense will occur).
Sure, but you use the fuzzy logic to come up with a
number. That isn't the case in the heap.
I can define heap as "I'm comfortable with calling that a heap" and FIRE as "I'm comfortable retiring on those assets". I don't really see how you can define FIRE any other way -- everybody chooses a particular chance of success that they are comfortable with, and there can be no objective bright-line guarantee that any particular person will not run out of money. Just because there is fuzzy logic involved in FIRE doesn't mean it's not possible to FIRE.
FIRE: "I'm comfortable retiring on these assets because I have historical expenses, researched how expenses change in retirement, projected out the length of time things should last, have estimated various inflation scenarios, etc. etc. and that means I need $X annually, and these assets should give me the $X I need based on X, Y, and Z research."
HEAP: "I'm comfortable with calling this a heap because..." ???
I don't have any
reason to call something a heap or not. I do have reason to think a certain FIRE number will be sufficient.
By the way, in real life do you actually look at a pile of bricks and say to yourself "well, I can't really say it's a pile of bricks because of the sorites paradox"?
There aren't a lot of bricks in my life. But yes, if I saw a pile of them and someone asked if it was a heap, and I actually paused and thought, I'd have to ask them what they meant by heap. Just because we are often careless with language doesn't make precise language invalid.
(Also, BTW, I'm really enjoying this discussion. Thank you dragoncar.)