Yes you can do that. Just don't stick it in soil and expect miracles though. Make sure you keep it moist and keep the humidity high. Too wet will cause rot, too dry and it will dry up faster than you can say "bye-bye begonia".

Here is an example where I used a little potting soil in the bottom of a lettuce container, barely dampened the soil, and stuck various leaves in like you want to do. Some did rot but none dried up and blew away. Put the lid on to keep the humidity high and place under lights or close to a bright window. You should see leaflets in a couple of weeks if all goes well.

Is it really as fast as a couple of weeks?

You should see roots and maybe little nubs of leaves starting in two weeks. They may sit there a long time after forming to go on to become mature plants though. The choice is yours when to pot up, fertilize, etc. to get them to grow to much bigger plants.

Here is an example of a plant that I got two little pieces of leaves of, stuck in a two inch pot. Two years later it is in a five inch bowl pot. This was taken on the 7th of this month.

Do you grow these as a hobby or to eventually sell them?

And im so worried about getting the soil to the correct amount of dampness without it being too wet or too dry.

I could not find a photo of the two little pieces as they were in mid April but here they are a month later (May 17, 2013). So in one month you can see they put on quite a bit of growth from two little squares of leaf tissue.

As a hobby. Don't fret too much about losing anything - no one gets it perfect to begin with and even with years of doing this I still lose plenty (too many to take care of so I don't obsess over them anymore).

Here is one of the easiest ways I know of to get a bunch of cuttings to put down roots. The Jiffy pellet greenhouse. The problem is there are 72 pellets in this tray so that is a lot of plants to pot up when ready and you must have space, lights, and time to care for them all. Then when you find this is so easy you start another 5 to 6 full size trays, you must be truly crazy.

The nice thing about the pellets is even if they seem to be soaking wet at times, they must have enough aeration to keep the roots growing.

If you are just doing one or two, get a small pot with good draining potting soil, moisten the soil, stick your cutting, and put a small plastic cup over it for a humidity dome.

Here is an example of a rhizome I was about to lose - I did not want to sink the rhizome in the soil as it may rot so I laid it on top of the surface and covered with a cup. It finally sent up a leaf and I believe sent some roots down as well.

Wished I could post more than one pic at a time.

And here it is uncovered.

One more for the road. Another spinach container filled with a little soil. You cannot see the two very large green leaves in there but the little green ones on the right side are from the big leaf under all the rest of leaves on the left side. I put this down from a friend back in August but am unwilling to move it out this time of year so it will stay until spring. The rest of the leaves have been added over the fall months. I dropped the container and probably ended up kicking it as well (by accident - clumsy big feet) which disturbed the soil but no harm done. Just shook it a little to settle everything and put it back under lights. The first two big leaves were started outdoors in this container in the shade. No water has been added since I started it - the moisture from the leaves and whatever was in the potting mix is all it needed. Easy? You bet. The problem is separating everything later on - it always puts stress on the plants.