I completely agree. But I there's a middle ground between "nothing you do matters" and "you can accomplish absolutely anything if you put your mind to it". People at either extreme of the spectrum are more likely to end up disappointed with their lives than someone in the middle.

I have just decided to be four inches taller than I am /s.

I have depressed friends that I believe can’t reasonably be expected to just decide to “do”, and I have other friends that seem to naturally have an abundance of “do”.

Yes, we can learn the skill, or we can be taught the skill, but otherwise your statement seems unrealistic to me.

I think one important thing that we, as a society, need to respect is that the amount of "do" it takes a given person to do a given task is very different from the amount of "do" it takes another person to do that same task.

For example, it may take somebody who's depressed the same amount of "do" to get out of bed and eat a yogurt as it takes a go-getter, "neurotypical" [0] person to get up, cook a healthy breakfast, go to the gym, take a shower, get to work, and get through their first couple tasks of the day.

[0]: I put "neurotypical" in scare quotes because I'm not sure neurotypical is even really a thing, it's just the term we use for people whose mental makeup fits well into our society and work culture.

IMO both you and GP are correct, ultimately whether the decision to "do" helps or not relies on individual circumstance and context plus on chance factors.