We are a lot like that glass and the onion combined. Each layer of the onion is filled with bubbles. Those bubbles are subtle beliefs (I can't trust people) (I'm not supported by my family) etc. we hold these beliefs as truths and never give them a second though. In fact sometimes we are sure we DON'T hold them, that we've healed from these kinds of situations. Yet they are there.
In tapping you make a negative statement and reinforce that you love yourself anyway! an example: "Even though I don't trust people I love and accept myself and allow myself to be." Is one such statement. Some folks might think that stating things this way is reinforcing the negative belief, but that's not the case. The negative statement is like tapping the glass and those bubbles that resonate with that statement are released and float to the surface, thus being released. The secret is to pay attention to your body so you can recognize what that feels like for you. Do you tingle, burp, itch - just notice how your body releases and keep tapping as long as your body is responding!
I can teach you how to tap using SKYPE or you can learn on your own by going here. There is a lot you can learn about how to use tapping to healing, eliminate habits and beliefs and more! It is one of the most useful and wide-ranging methods I know.