Read the first chapter of Genesis where God talks about "seed." Essentially the seed of something always produces the like kind. A dog seed (sperm) will always produce another dog, a cat seed (sperm) will always produce another cat, etc.
Adam became a sinner when he disobeyed God. What, then, would his offspring be? Another sinner. What do sinners do? They sin!
Put another way, we are not sinners because we commit sins. We commit sins because we
are sinners. We are just acting out our nature. Dogs bark, cats meow, and sinners commit sins.
Our individual sins are not the problem. The problem is our sin nature, which we inherited from Adam.
Rom 5:12,
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
Death was not in the world until Adam sinned. Unfortunately, we are all left to share the consequences.
The solution?
Rom 5:15,
But not as the offence, so also [is] the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, [which is] by one man, Jesus Christ, hath abounded unto many.
One man's sin makes us all sinners but one man's death (and resurrection) makes us all saints. Yeah Jesus!
The above also explains why Jesus was different than all other men. He did not inherit the same corrupted seed as all other men. Instead God miraculously implanted a brand new seed that did did not come from sinful man, but from God Himself. Of course it was up to Jesus to keep himself sinless by always obeying God, something Adam failed to do.
God bless.
Just kidding.