lots of good points here! Fastdogs makes a really essential one I think, that the trial you THINK you're riding may not be where you actually are...and that's inevitable, some of us are lucky to have reliable trail maps for some areas, and some days you just have to leave early enough to make sure you have plenty of daylight to find your way home just in case......

As someone who regularly rides anything between beginner and advanced with varying success...my best recommendation is try to find someone to ride with who knows YOUR riding style. or if you love "trail A" ask around to look for similar rides. Although I think a part of mountain biking is having those "walked it half the ride" days. If nothing else it keeps you humble and don't let it make you feel bad, that happens to ALL of us. Hiking with 30lbs of bike is a good workout too