The gym sucked today… I had to throw my plan out the window…
Here's a great answer to the question Do you need a workout plan?
That's the truth,
If you need structure, maybe you do.
Or you crave variety and being surprised then having no set 'plan' may work better for you.
Either way, you need to show up and work your ass off consistently.
You can be one of those guys with the little notepad, writing down every set, weight and exercise. Or you can go into the gym and wing it all the way from your warmup to your workout and cooldown. You do a cooldown right? I didn't think so.
I've had great training plans and made progress. I've also had no real plan and made progress.
Depending on what you want to get out of your training, you may need to track your workouts and stick to a plan. There's some flexibility here too. The best plans allow for changes to be made over the course of the weeks/months.
There are a million ways to structure a workout/plan so I won't get into that here.
I'll leave you with this. You should try a program at least once. Stick to it for 3-4 months. If you hate it or just don't like being tied to a single program then you've learned some valuable information.
You don't always have to have a goal with your training. Fitness is good enough on it's own without a specific goal, but if someone has a burning desire for a goal, then I say go for it with all you have!