Vegetables all need room to grow, right? Certain vegetables, particularly beets and swiss chard (two of my favorites) often sprout more than one plant out of a seed. Even if you seed to the correct measurements on the pack, i.e. 4 inches apart, etc. you often have this situation.
Bull's blood beets - 5 seedlings within 3 inches = not going to work
Merlin F1 Hybrid Beets - the weaker/smaller one has to go
The beets then will grow their greens (also delicious) but will form a stunted skinny bulb because it doesn't have enough room under ground. Same problem with carrots. The trick with thinning though, is getting just the seedlings you want out. Sounds easy right? The problem is the seedlings are so close that it is very difficult to pull one, without dislodging or damaging the one next to it. Their are two options; 1, be very very careful, and pull slowly requiring a lot of patience 2, use manicure scissors to cut out the seedlings you don't want. Either way it's a ridiculously tedious job