When the consequences are severe, people learn quickly. - James Clear

Mental toughness immediately increases when you find the right subject. You're more likely to stick with things when you're genuinely interested.

Study as if you know nothing.

Work as if you can solve anything.

"Happiness is simply the absence of desire. When you observe a cue, but do not desire to change your state, you are content with the current situation. Happiness is not about the achievement of pleasure (which is joy or satisfaction), but about the lack of desire. It arrives when you have no urge to feel differently. Happiness is the state you enter when you no longer want to change your state.
However, happiness is fleeting because a new desire always comes along. As Caed Budris says, “Happiness is the space between one desire being fulfilled and a new desire forming." Likewise, suffering is the space between craving a change in state and getting it.