Buying players with the highest quality per price ratio is the key. Buying hyped youngsters isn't as crucial as it was ten years ago, as players and agents are having too much power in negotiation. Their salary is too high too early. It does not matter how young a player is, if we can't afford they will leave, and the owning team isn't getting much out of that.
Look at the Milan youth project for example. They could nurture the best youngster on the planet (Donnarumma). They could suffer players' mediocrity for years (Kessie, Hakan) just to see them leaving as soon as they polish. For 0€. Even worse, that kid cannot develop as expected and the owner has to be stuck with him for a long time (Romagnoli). The younger a player is, the more expensive the cost is and it adds up to the burden of risk.
Inter is having the same issue but in a lesser extent. Brozovic is at his prime but we are still losing him for free, because of his 8m€ demand. Lautaro is super young, only 24yo, but as soon as he will ask for a payrise, already out of our affordable range. We can't keep regardless.
Ofc you can find kids that love the club and are willing to play with relatively lower salaries, like Skriniar, Barella, Bastoni, but those are extremely rare. It would be less risky to squeeze older players their best years, pay them exactly when we need them and let them leave soon enough. Like Young, Moses, Dzeko, Vidal. In the worst case, a massive failure like Kolarov costs us a fraction of damage compared to what Joao Mario did.