Mistake

I'm the type that make mistakes during those huge and serious projects, especially at the time when my things going to install or delivery to my customers' place; but, most of the times and luckily i can settle it and pass it on time. I wonder why it always happen on me, am i too careless? Or, lack of working experience? I don't know, but i'm still trying to minimize this mistake, yes, I DO~!!!! Lately i've been dealing 2 projects which about whole office open plan system (partition things ok?), even the carpet too. 30K not a big deal, but still money, who cares those so called big big company, but always proud of their so called WELL KNOWN company which always need terms for 30, 60 or even 90 days. Well, just say something about my job here. ^___^