When training in the gym, I rarely ever set myself (longterm) goals for my lifts. Or when I do, I most certainly don't reach them, what demotivates me. Is there a good way or method to determine realistic goals? So goals that are challenging in order to motivate while training but at the same time doable to achieve?
This will depend heavily on what you're training for. I personally set few, but hard to achieve goals per year. And with few I mean things like, I want to be able to deadlift x-amount (right now I'm shooting for deadlifting 3x my own bodyweight) or I want to be able to do a one-arm handstand (my main sport is calisthenics).
These are very hard but achievable things if you work hard. It helps me focus to become really good at one thing, rather than being mediocre at everything. I understand that this is not for everyone, but it's an example of what I do.
As I said, setting goals depends on what kind of sport you're doing.