Being skeptical
Since I was a very young child, my family used the parable of "Doubting Thomas" to describe my constant questioning and skepticism- never in a positive light. In the event you are not familiar with this particular biblical story, the Apostle Thomas doubted that Jesus was truly resurrected, and demanded to probe the wounds in his side before he would truly believe the other Apostle's claims. Upon seeing Jesus wit his own eyes, and the wounds in his side, Thomas was no longer a skeptic.
This particular parable goes on to detail how Jesus told Thomas that those who believe but have not actually witnessed are "blessed". I prefer to call them stupid. Being a skeptic does not mean I do not believe something I have not seen physically, but rather that I will not believe things that have no evidence to back their claim.
An example of my belief would be that the earth is, in fact, a sphere. I have not personally been in space to witness this particular fact, but I see evidence all around me. When a ship sails into the distance, it appears to rise, then sink below the horizon. This is a classic sign that we are on a sphere. Another fact that I believe is that astronauts have visited the moon. Again, I did not personally witness this event. In fact, I hadn't even been born yet! But the evidence to support the claim is so overwhelming that not believing would be ludicrous. It would probably also get Buzz Aldrin to punch you in the face.
Conversely, however, there are more than enough claims that I do not believe. Extra terrestrial beings visiting our planet is one of them. To the best of our knowledge so far, there is no way a living being could cross the universe's vast expanses in a lifetime. For that matter, crossing interstellar space would take several human generations! To cross the distance our radio signals have traveled in 100 years would take our current space vehicles 27,254 years (299,792,458m/s / 11,000m/s = 27253 years). Without some kind of physics altering technology, this is as near impossible as we care to conceive of. For perspective, this is about 10% of the entirety of human history.
One more claim I disbelieve without evidence is Homeopathy. This is the idea in alternative medicine that you can dilute a particular substance in water to non-existence, but the water will "remember" the original substance. When you ingest this water, your body uses like compounds to treat like ailments. As an example, you can take bee venom, dilute it in what is the equivalent of more water than the earth contains, and drink a vile this solution. Your body will now magically treat itself for bee sting allergies. If I know you personally, and you are allergic to bee stings, PLEASE do no try this. At the least, you will die from your sting.
The world is chock full of cheats, scoundrels, liars, and deception. To not be skeptical about claims made by others is to ignore the very thing that separates humans from the rest of the animal kingdom- complex reasoning skills. If I tell you that rainbow's are made by Leprechauns hiding pots of gold, but you learned in science class they they are made from light hitting water, which causes a prism effect, who will you believe? The simple answer is to do a simple test- use a water bottle to spray some water into the air in a fine mist. When you see your rainbow, look around quickly for leprechauns. If you don't see any, and you can reproduce this result time after time, chances are that leprechauns are a lie.
The moral of this story is that I am, in fact, a doubter. I am a true skeptic, and I have been since early childhood. I take that as a sign of a healthy, inquiring mind that is thirsty for knowledge. I also look at those that do not have this same inquiring mind to be ignorant, or at the very least unwilling to expend the energy it takes for simple fact checking. And in todays world, the stakes could not possibly be any higher.