Where do I start!??
Mentally prepared but giving up easily? I think it's totally opposite. Look, yes at first you'll break down easily but as you progress and you gradually do it, you'll see good results and motivate yourself more. Plus, you'll notice that you aren't the same as you are yesterday. So my suggestion is choose the workouts where you will enjoy. And just get your ass working! Good luck!
I would like to suggest you train as much as you can, depends on your expectations. If you want to be ripped, you have to train like warrior and eat clean.:-)
I just also started, try those 5 min workout, then increase a step at a time.
in my opinion, giving up easily is total opposite of "MENTALLY PREPARED" !!!!! our will power and drive to succeed is 1st a mental challange. just bc your unhappy with the ways things are and want nothing more than to be healthy and fit, doesnt mean youre mentally prepared. its a mental prepared