Real constraints and self-imposed constraints
There are two worlds in which we live: Mundia and Modia. In the world of Mundia, laws are physical. If you jump, you will come down. If you push something, it will fall over. In the world of Mundia, many things are possible. If you see a new shiny object that you want and it's not glued to the ground, you can pick it up and take it home with you. In Mundia, things follow physical, immutable laws.
In Modia, our laws are social relationships. Jumping doesn't matter there, except if you can jump really high or really far, in which case someone will give you a gold Olympic medal that we have decided has Modian value. If you push someone, and they fall over, you will likely be disliked by that person. If you see a new shiny object that you want, you can't pick it up and take it home with you unless you hand over some money for it, which we have also decided has Modian value. In Modia, things follow laws that everyone who lives in Modia has agreed to follow.
"Cannot" has an impossible-to-dispute meaning in Mundia. It means the laws of the world prevent you from doing something. Only 0.00001% of everyday constraints are Mundian in nature.
"Cannot," in Modian terms, is mostly a shorthand for "the intensity or volume of actions I/we would have to execute in order to get this done is undesirable for the value I would derive from it." For instance, Mundian law dictates that I can delete every email from every email account in the entire world. It's possible. Modian law says that if I did this, I would be thrown in jail before completing my mission, which is undesirable to me.
There are very few real constraints in this world. Most of the time they are self-imposed.
When I was in college, I met a person who knew at 18 that he wanted to live the LA celebrity lifestyle - but he wasn't a good actor, or musician, or writer. He was an accountant who liked playing with numbers. Most accountants don't end up hobnobbing with Katy Perry, except for this guy... who figured out how to go be her accountant. When Katy Perry has a question about how her stocks are doing, she calls this guy. And when Katy Perry hosts a house party, she invites him out.
Accountant Guy thought long and hard about what he wanted and how to get it under Modian Law. He couldn't offer anything of value on the artistic front. He didn't want to take years of his life trying to develop those talents, as it would cost him the fun years of partying in LA. But he was good with numbers and a responsible individual, so he learned how to be an accountant, built his quals up in the entertainment world, and pushed until he was working for the superstars.
The same is true with all applications of Modian Law. There is always a workaround. It may cost you more than you want. You may have to sit there and let the problem scratch at you for years. But there is always a way out.