Cuttings should not be expected to root in the full sun. With no roots to provide the cutting with moisture it will wilt and die. Al

I can vouch for that. And if you think you can keep the moisture in by putting a plastic bag over the cutting out in full sun, don't count on it. You'll just cook the plant because of the excessive heat greenhoused in the bag. It kind of suggests an interesting way to cook food using solar power. ;-)

Add to the list of no nos the fact that rooting may require natural triggers similar to what seeds require, waking from dormancy in particular, and you have yet more reasons to wait until early Spring to do your cuttings. Or for some plants, at least late fall.

That's not to say that you can't do your cutting in a more controlled environment, indoors. Nor does it say that you might have cuttings from some tropical that is not geared to seasonal dormancies. Nor does it say that there are not plants that will sprout from cuttings in direct sunlight. Potato Bush for example is one plant that I have found is extremely easy to propogate from cuttings. You just cut a small section of stem, push it into the ground, keep it moist and wait. Sometimes it can take months and sometimes a matter of a few days. Potato Bush cuttings love direct sunlight, but won't put out leaves until they've established roots.

Read carefully any advise on the length of the cuttings. Long cuttings may often fail because the plant apparently feeds on itself before putting down roots. Short cuttings seem to induce the plant to root more quickly. It's not magic. There is a plant mechanism that draws water and nutrients upward through the plant and you can't stop this, only limit it, by making your cuttings short. Folks with experience in a particular cutting recommend certain lengths - use those lengths.

Finally, some cuttings require the presense of a bud or other plant structure to be present on the cutting. Pay close attention to this requirement for your cuttings. If all you cut is stem in these cases, you will fail to propogate the plant. I'm sure you can find numerous examples of this.

Good Luck.