I’m formally trained in this subject and I find parts of replies to you as correct, while most are just outrageous.
First, you should define your goal. Do you want to be generally fit, or do you just want larger biceps? Can’t force you to be well-rounded and ask you to change your perception of beauty, so if you just wanted bigger biceps then go ahead and just do curls. Be warned though: other fit people are going to notice the imbalance in your body such as skinny legs, underdeveloped forearms, bad upper body posture, etcetera; and even your perception of beauty will change as you progress, so I strongly suggest that you do not train for just one muscle.
If you go for general fitness, start with the most basic compound lifts: barbell bench presses, either squat or deadlift, and then barbell rows (funny how no one mentioned this exercise, lol). These are the most essential movements involving the largest and most essential muscle groups that are used in any other exercise. And note how I speak of muscle groups — in order to perform a muscle contraction, you’re actually not just using a single muscle. You have prime mover muscles, and others are stabilizers, and you want to train the whole group by doing exercises in full-range of motion so that they are all developed, because that will keep you safe from injury when doing more challenging exercises with them.
If you want to know more about the whys, the subject that you want to study is called exercise physiology.
There can be certain beneficial imbalances for particular sports. Rock climbers tend to need disproportionately strong fingers, and legs focused for jumping rather than pure strength. Boulderers need more focus on legs than route climbers, mountaineers need more overall balance and endurance, etc. Too much imbalance can lead to injury (all lats no pecs would be likely to cause back pain, as would the reverse) but some can be useful for particular goals.
I disagree with the notion of “beneficial imbalance” here. It’s likely that we may be thinking of the same thing when I’m talking about “optimizing or specializing for a sport”, but I will never use my notion as an argument against training the essentials. You‘re not going to be a more successful (and more importantly, _safe_) rock climber, boulderer, or mountaineer without a baseline strength in the essential muscle groups because those will keep your whole body stable and your posture as it should be while you’re wiggling your body about vertical surfaces. Well-rounded baseline strength could very well spell the difference between life and death especially for the activities that you mentioned.
There’s also the fact that should rock climbers, boulderers, and mountaineers have lives and real jobs outside what they do for recreation, then the reality is that they have a variety of bodily movements that just need to be generally done with, again, good posture, which you simply can’t have with an imbalance in the essentials.
First, you should define your goal. Do you want to be generally fit, or do you just want larger biceps? Can’t force you to be well-rounded and ask you to change your perception of beauty, so if you just wanted bigger biceps then go ahead and just do curls. Be warned though: other fit people are going to notice the imbalance in your body such as skinny legs, underdeveloped forearms, bad upper body posture, etcetera; and even your perception of beauty will change as you progress, so I strongly suggest that you do not train for just one muscle.
If you go for general fitness, start with the most basic compound lifts: barbell bench presses, either squat or deadlift, and then barbell rows (funny how no one mentioned this exercise, lol). These are the most essential movements involving the largest and most essential muscle groups that are used in any other exercise. And note how I speak of muscle groups — in order to perform a muscle contraction, you’re actually not just using a single muscle. You have prime mover muscles, and others are stabilizers, and you want to train the whole group by doing exercises in full-range of motion so that they are all developed, because that will keep you safe from injury when doing more challenging exercises with them.
If you want to know more about the whys, the subject that you want to study is called exercise physiology.