Once you're physically in the gym, working out is not that difficult.
You may not feel like it, or maybe you're sore, or maybe you’re just not motivated for that session. But if you're there, you will do something.
The hard part is actually showing up to the gym. Getting up, getting dressed and driving/walking/biking/riding the elevator to the facility is the hard part. This is the part that separates the average gym users from the ones about which we say, "I wish I had your motivation".
Once you conquer the showing up part, getting muscles/getting skinny/getting in shape is much less difficult than it seems. You can probably understand that the gym can be a metaphor for anything else in life, too.