Many Christians are preoccupied with sin, and some of them are that way because they are trying to better their lives. This is a good idea on one hand, because the more familiar you are with sin and what it means to sin, the more enriched your life can become because you can rise above typical human behavior and free yourself of as much sinful behavior as possible. The unforgivable sin is something altogether different, and something that your typical Christian doesn't give all that much thought to.
The unforgivable sin is denying Jesus Christ. It's said that this sin cannot be forgiven, or that is how scripture in both Mark 3 and Matthew 12 has been interpreted for a long, long time. Of course, every good Christian knows that you have to accept Jesus Christ into your life to be forgiven for your sins, since it is Jesus Christ that for our sins. Most Christians do not concern themselves with the unforgivable sin because they have accepted Jesus Christ into their lives and consistently ask for forgiveness when warranted.
No human is free of sinful behavior. We can all be judgmental, and we do this without even thinking about it! Our experiences change us, so that we are judgmental to a certain extent, but as long as we are aware of this behavior and ask for forgiveness, we will be forgiven. Becoming aware of the sin is as important as asking for forgiveness. When you ask for forgiveness for a sin you are actually growing as a person because you can see the wrong in what you have done, how you have thought, or what you have spoken to yourself or another person.
Many serious Christians are afraid to sin, and while you shouldn't aspire to behave in a sinful way, it's a learning experience. When you act inappropriately and you acknowledge it through prayer or asking for forgiveness, you grow as a person. Each time you sin and acknowledge it, you are overcoming a negative piece of who you are, or a not so great aspect of your life. Sin is natural, and while it is something that many fear, it shouldn't be, as long as you are willing to ask for forgiveness. When you sin you should think of it as a chance to grow, to become a better person, and perhaps even inspire other people to live life the best way that they know how.
If you worry about committing the unforgivable sin, it's likely that you needn't worry. The unforgivable sin isn't as simple as wondering what Jesus and God are really all about. Almost every person out there will tell you that at some time in their life they have questioned the extent to which they believe in Jesus Christ and allow him into their life. The thing is, most people overcome these questions and even ask for forgiveness for questioning the love and relationship that they have with Christ.
So, if you sin, relax and realize that everyone sins every once and again. Don't beat yourself when you believe you may have acted inappropriately, just chalk it up to a learning experience and ask for forgiveness. If you give yourself some room to mess up, you'll find that you can actually grow as a person, as well as foster a great relationship with Jesus Christ.