Answer:
1. To say "thank you" or "please" is to empower the other individual for choosing to take action vs. being told to take action (and having no power)
As with all creatures, humans are programmed to seek freedom; the freedom of choice most powerful of all. Over hundreds of years and most likely heightened in the Industrial era boom, we've moved away from the individual model of society (where people primarily worked for themselves) to the institutional model where large organizations dictate our work (and personal) lives. In essence, when you say "please" or "thank you" you are asking and then thanking the individual for making the choice to take on a task or activity. Contrarily, when you don't say please or thank you to someone for a task, they feel like they had no choice in the matter and thus no power. Which leads to appreciation...
2. People need to feel appreciated and loved
Human beings are sensitive creatures, more so than any other animal because we're one of the few (if not the only but perhaps dolphins too based on studies) that have consciousness (feelings, thought, etc). By saying "thank you" you're also saying "I appreciate you". It's so simple and effective.
3. Making others feel good brings good in other unpredictable ways
By making someone else feel important and appreciated, you've brightened up someone's day in the smallest of ways and that person is more likely to pass on that feeling to someone else. If they feel dejected and under-appreciated they tend to take it out on those close to them (spouse, kids, friends, etc). The act of saying thank you is also powerful in that it makes people more willing to do something for you again in the future. Creating a cycle of goodwill is essential if you believe in karmic energy ("what goes around comes around").
4. Saying thank you is the simplest form for practicing gratitude
I wrote about the importance of gratitude here. Practicing gratitude is the #1 way to be happy (it's a choice FYI). If you're having trouble with your mental state of mind then start crawling before you walk by saying thank you to anyone and everyone. The act will make you feel better and as with #3 will benefit you in unpredictable ways as it will the recipient.
Explanation:
Hope tis helps
