If you have ever struggled to lose or gain weight, I guarantee you have at some point heard the advice: 

“You just need to eat more/less than you burn”

The person that typically says this kind of thing most likely also holds the belief that being overweight or having obesity is a result of pure laziness or a lack of morals. At the surface level, this advice is correct. However, it is correct in the same way that going to a football game and telling the head coach of your team “Hey pal, you just gotta score more points than the other team and you’ll win” is correct. Correct, but very unhelpful and lacks any understanding on what contributes to the scoring of points. 

3 things will optimize your muscle gain: Resistance training, A calorie surplus, Adequate protein intake.

Each of these things plays off of one another. You can gain muscle in a calorie surplus without resistance training, but you’ll likely put on more fat than you will lean body mass if you don’t lift. If you don’t eat enough protein, you won’t put on as much muscle as you could.