"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
Just as much as we humans are what we eat, we are what we think. Eat junk, feel like junk. Think junk, be junk. I have never met a person who talks (or thinks) negatively about themselves and also has a positive outlook on life.
We all have a tape player in our mind, endlessly looping a stream of conscious (and even more dangerously unconscious) thoughts. If we find ourselves feeling down or anxious, it's really important in those moments to step back, be quiet and examine our thoughts. Often times, those thoughts aren't quite true. That's not to say that they aren't based in some truth, but often times, we blow things out of proportion.
It goes something like this: Say you have a job interview coming up and you are feeling overwhelmed/anxious about it. There is a good chance that the thoughts going through your mind in that moment aren't, "I am well qualified for this, I'm such an awesome person that the interviewer won't be able to resist hiring me, I have so much to bring to this company that not hiring me would be detrimental to their fiscal future, etc." In the moment, our thoughts are probably more like, "I just barely meet the qualifications for this job, I have such little experience in this field, I'm going to bomb this interview, etc."
2 Corinthians 10:5 says it like this in the NIV (emphasis mine), "We demolish arguments and every pretension that sets itself up against the knowledge of God, and we take captive every thought to make it obedient to Christ." Let's use this verse as the first step. Sometimes its hard to know what to do with that negative thought after you recognize it. A negative thought such as, "I just barely meet the qualifications for this job," requires a bit more observation. Once you have taken your thought captive (recognized it), take time to examine it; write it down, study it, ask yourself if you have heard this sort of talk before and if so who was it coming from? I have spoken with many people who've said these sort of things (myself included) yet didn't see the underlying assumptions. "Not qualified" could possibly assume: worthless, a bad person, incapable, failure and so on.
Please challenge your negative thoughts. Write out a list of reasons your aren't a "failure," "bad person," or whatever. Ask a friend for some help making this list could be extremely beneficial. When you commission a friend, you can hear it from someone outside of your own voice which in turn, can make it easier to believe.
I'm sure I have sabotaged my own fair share of opportunities by my negative thinking. When life gets hard, we can't just throw up our hands and think, I guess I'm just not cut out for this. We have to think positive and continue forward. Set backs are a given, failure is faulty thinking.
Now let's broaden this out to physical fitness. If you want to get into shape, what sort of things are you telling yourself about starting? I often hear, "I will never be able to lose the weight and if I do, I wont be able to keep it off", "I just can't find the time during the day to fit it in", "Gym memberships cost too much money," etc. etc. etc. Sabotage after sabotage after sabotage.
The scariest piece of this whole puzzle is this: we do have what it takes to get the job we want, to be in shape, to live the lives we want to live, we just have to rid ourselves of the negative self talk, replace that old worn out tape player telling us we are no good, and start being the people we were designed to be.