Suppose you tried to be a really good person. So you decide you will only sin three times a day. Just think how good you would be. Maybe you only say one thing wrong ALL DAY! And you only think one bad thought during the whole day! And maybe you only did one thing wrong each day! You'd be pretty proud of yourself wouldn't you? I mean, that would be a real accomplishment considering the thousands of thoughts we think in a day or the thousands of words we speak in a day. Just three sins!
BUT....if you multiply those three sins by 365 days in a year you've commited over 1,000 sins! And if you were to live to be 70 years old you would have commited over 70,000 sins in your lifetime! And that is the result of trying to be really, really good. You can imagine what the actual count really is in a person's lifetime!!
The Bible says if we want to get to Heaven by being good we need to be perfect, not even one sin, Matthew 5:48. It also says that all have sinned and come short of the glory of God, Romans 3:23. None of us can get to Heaven in our sinful condition. But Jesus lived the perfect life for us. God loves us so much He came and died on the cross and took the punishment we deserve for our sins upon Himself.