Why do I always say that communication is the key?

A thread.

Why do I believe that communication is the key to every good relationship?

Because it is.

It really is.

You have a problem with your friend. You FEEL that they don't talk much to you now.

Did you ask why? No.

You already assumed. You already formulated things in your head like, "They don't want to talk to me anymore because I am not a good friend. I am a loser."

You have a problem with you parents.
You FEEL that they are unfair and they are very strict to you compared to your siblings.

Did you ask why? No.

You already concluded that, "They love them more because my siblings are smart and top notchers but I am stupid and useless."

You have a problem with your partner.
You FEEL jealous because they are very close to one of their friends, specially opposite sex.

Did you ask why? No.

You already imagined that they are doing something behind your back and your partner is already cheating on you.

Why do problems usually arise in a relationship? Because you assume before you even ask. You let your imaginations do their work before talking to the person involve.

Remember the golden rule in Accountancy:

Never assume unless otherwise stated.

"Siguro," "Baka," "Maybe," "Feeling ko," "What if,"

-- Those are all assumptions. And if you keep thinking about those, you'll surely get crazy and relationship will get broken. You have to talk to the person involve. Communicate your feelings and be true and honest.

Your friends talk less to you because they got busy at some point, or they are sad and lonely they don't want to affect your mood with their feelings, or they got shy because they forget to reply to you, or they just really don't wanna talk to you

Your parents take extra care of your siblings because their health condition is not good. They are usually weak and get sick easily but you are the strongest among them and you are very independent. Your parents are so thankful because you stand as their best older sibling.

Your partner is not really cheating on you. Your partner is just really close with their friends, or your partner is really cheating on you.

There are millions of possibilities. It may be good or bad. How will you know if you will not communicate, right?

Base your next steps with FACTS and not just ASSUMPTIONS. If it's a continuation of something good or ending of a relationship, at least you are SURE.