I'm feeling a bit disheartened today. I'm wondering if I have a setting or something wrong with my camera or if I am doing something wrong when taking a picture.

Yesterday I went out for 6 hours walking amongst the rain forest on a overcast sort of day and played with the manual settings and took a few shots of the same thing with different aperature and shutter speeds to practice and learn what is best. So doing landscape type pictures. I've taken over 80 shots and I know not all of them are going to turn out well, but I do remember looking at my screen after the shot had been taken and thinking yep, perfect! It looked like a great picture and I was really quite chuffed.

Now I have come home and looked at the pictures on the computer and I'm disappointed. A lot of the pictures are out of focus for some reason. Whether I have used the wrong settings I am unsure. I do use a central focus point, but maybe I just haven't got my composure correct. This is all fine, but the thing that is really bugging me is that they all looked fine on the camera at the time! If they hadn't of course I would have retaken the picture. Those two or so pictures I thought would be the best, I can't even seem to find. *sigh*

So I guess my question is why is the screen picture not telling me the truth? Should I ignore it all together or is there a setting to change? Does anyone have any help for me??
Oh... and I am using a tripod now.

Thanks.