Make sure when you embark on a training program that it's something you can sustain...day-to-day...month-to-month...year-to-year. Always err on the side of doing a little less. Nothing kills training more than overdoing. If you can't sustain it, don't start it. This applies to everyone...not just beginners.
You should end most workouts itching to do a little more. Rarely should you be totally spent. Driving yourself to exhaustion on a day-to-day basis may work in the short-term...if you survive...but over time, your mind, body, and spirit will rebel and eventually you'll be back to square one...wondering why you even started in the first place.
Using running as an example...in all my years, I do not think I have ever seen someone who broke down or "failed" with a training program because they ran too easy. People mostly quit or get poor results because they do not train regularly enough. Usually they quit because they are simply running too hard.
Several years ago there was a women in our running group that took the train easy method to heart. So much so that I thought...you know, here is finally someone who I can honestly say is training too damn easy. She was very timid. In fact, I think she was actually afraid to run fast. She would pitter patter along and I'd think...geez, she is really dogging it. But she was still improving. No one disturbed her. Jumping ahead to the present day...she has improved by leaps and bounds. She often places in her age group at local races. Last year, she ran her first marathon. She even coaches her own beginner's running group...and is quite good at it I must admit. Her name is Susan Eastman.
So relax...take your time...dream big...but set nice, achievable short-term goals. As long as you take small sure steps, nothing can stop you and you'll get to where you need to go.
And if you screw up...get up...dust yourself off...and begin again...this time a little bit wiser.