I think for most people being functional as an adult in society requires a large initial investment of time, effort and energy.
It can feel like you're at the bottom of a never-ending staircase of things that need to be done: studying, networking, passing exams, working small jobs, building more work experience, selling yourself in interviews etc and these things all take effort and struggle. It seems daunting to think that you'd have to work that hard all the time for the rest of your life. But then the hope is that after that large initial investment of energy actually things become slightly easier. Exams passed, employed in a job that pays a liveable wage, have a place of your own to call home. And suddenly there's momentum behind you and solid footing beneath you. Perhaps instead of a never-ending staircase, it's more like just getting up to speed in a car. Yeah you need to put in a lot of energy to accelerate and get up to speed but once you're actually at speed it requires a lot less effort to maintain it. Once you get over those initial hurdles you're just coasting along; attending a job that you know how to do and following a monotonous routine.
I look at people in their 30s, 40s, 50s with jobs that pay a decent wage and I think surely these people cannot be expending maximum mental effort all the time. No doubt they put in hard work to get to that point but it looks to me like they put in an initial effort (sometimes over a good few years), get to a certain level and then once it's self-sustaining they can carry on indefinitely until they die of old age or whatever.
But to tie in to your question, how hard that large initial investment is going to feel must vary from person to person. All well and good for me to type it out but I've not been able to do it and I'm sure it's the case for many of us here. I think there's "laziness" and then there are other, deeper, things holding people back. To feel that you cannot take the steps required to get a solid foothold in life is quite an overbearing feeling. And then to think "well if I can't sustain myself then what will I be facing?" Homelessness? Starvation? Freezing to death? And that's when the idea of suicide can seem preferable, at least for me.