Most people undertake a project with an illusion of how much time and effort it will entail. Sooner or later they become disillusioned. That’s actually good news. Disillusionment means that they are ready to start making decisions grounded in reality.
Being disillusioned doesn’t make you a pessimist…it makes you a realist. There’s a big difference. A realist sees things as they are and then makes a decision. Give me a tenacious realist over a delusional optimist any day.
Don’t confuse illusion with vision. Illusions are fun and sometimes even inspiring but they are also deceptive because they create a false impression of realty…that’s dangerous territory.
Next time someone asks if you are pessimist or a optimist, tell them you are neither…tell them you are a realist.
“The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.” William Arthur Ward
markbartels.org 
The whole reality distortion field concept kept side tracking me. I ended up concluding the reality distortion field is more about Vision than an act of illusion or over optimism
Also, the disappointment is the difference between reality and expectation. Therefore the more realistic you can be about the project, the less likely you are to be disappointed and consequently you are less likely to give up.