They are right, I didn't. However, for someone who couldn't run a 1/4 mile or do 10 push-ups at the start of my exercise doing 3 miles and 50 push-ups is awesome! It's unfortunate that most of society seems to press us to either put-up or shut-up in this regard. The goals you set for diet and exercise should be attainable goals that you step up over time.
Working on losing weight or toning up? Go back and reread that last sentence. The keyword being "you". You cannot let others dictate your goals. You want to work up to Marathon or drop 100 lbs, great! Work toward it, but make sure that you work toward the goal over time. Why? Unless you have a lot of dedication, focus, and discipline when you hit that first "I can't do it" plateau, what you'll see is the distance between where you are and that marathon. Most people will give up at that point - "It's just too much".
Aye, but you can do it - just break it up. Twain said it best;
The secret of getting ahead is getting started. The secret of getting started is breaking your complex, overwhelming tasks into small, manageable tasks, and then starting on the first one.How far can you run now? Good, do that for a week. Then increase it over time. Working to a marathon? Use one of the training guides to help you focus and build up over time, no one does this over night. However, most people are going to expect you to.
As for me, I'm following the Phase 1 BUDS (Navy Seals) Suggested Student Preparation at the moment. I'm dead on for where I should be given the goals I have set for myself. That, more than anything, is what's most important.