There's a joke that Kimi ni Todoke (aka From Me to You, aka Reaching You) should be subtitled "Misunderstandings: The Anime." And honestly, it's true. There's another anime (Say I Love You) where a lack of communication between the two main love interests plays a huge part in the problems that happen throughout the show.
I don't want to spoil things, but let me teach you why communication matters!
You intentions, no matter how clear they are to you, cannot always be clearly seen by others.
We see this especially in Kimi ni Todoke. Sawako is really, really sweet, but everything she tries to do that is nice is communicated poorly, and so everyone thinks she's terrifying! With the help of her new crush & friends, she tries to over come this, and we can learn that being able to communicate clearly is so, so important!
Just because you've been betrayed before, doesn't mean you'll be betrayed again!
Mei in Say, I Love You is a really likeable tsundere, but she struggles to get over the fact that she has been betrayed in the past, and so because of that, her relationship with Yamato sometimes suffers. Remember: not all people are the same! Be cautious, but don't block every one out & remain isolated because of fear ^-^
If you communicate with the person you're afraid is going to betray or hurt you, they'll be able to work harder to make sure they don't make you scared anymore, and you'll be able to feel more comfortable opening up to them. If you're seriously considering dating someone, you have to communicate the fears that are keeping you from doing so, or you'll never be able to make the relationship happen!
Just because you're shy, doesn't mean something doesn't need to be said.
Being shy can mean that you don't have to be as forward in your intentions as others and they should understand, but again I think we see this one in Kimi ni Todoke. Shyness doesn't give you a free pass to not speak up about how you feel! In Sawaka's case, she really doesn't realize she's being shy, but her staying quiet because she felt she had to led to a lot of problems that wouldn't have happened had she simply spoken up and said what she was feeling!