they think they suffer because of their sin or its inherited from your parents or its the result of free will.
If by suffering you mean persecution, then it is a reality for many Christians in the world in various forms, especially in countries with repressive governments and few freedoms. Martyrs are being made as you read this. See the Web Link to the left. None of this should surprise a Christian though, as the following verses point out. Christians should not pity themselves, but understand the underlying reasons.
16 Behold, I send you forth as sheep in the midst of wolves: be you therefore wise as serpents, and harmless as doves. 17 But beware of men: for they will deliver you up to the councils, and they will scourge you in their synagogues; 18 And you shall be brought before governors and kings for my sake, for a testimony against them and the Gentiles. 19 But when they deliver you up, take no thought how or what you shall speak: for it shall be given you in that same hour what you shall speak. 20 For it is not you that speak, but the Spirit of your Father which speaketh in you. 21 And the brother shall deliver up the brother to death, and the father the child: and the children shall rise up against their parents, and cause them to be put to death. 22 And you shall be hated of all men for my name's sake: but he that endures to the end shall be saved. 23 But when they persecute you in this city, flee into another: for verily I say to you, you shall not have gone over the cities of Israel, till the Son of man be come. 24 The disciple is not above his master, nor the servant above his lord. 25 It is enough for the disciple that he be as his master, and the servant as his lord. If they have called the master of the house Beelzebub, how much more shall they call them of his household? Unto you therefore which believe he is precious: but unto them which be disobedient, the stone which the builders disallowed, the same is made the head of the corner and a stone of stumbling, and a rock of offence, even to them which stumble at the word, being disobedient: whereunto also they were appointed.
For what glory is it, if, when you are buffeted for your faults, you shall take it patiently? but if, when you do well, and suffer for it, you take it patiently, this is acceptable with God. For even hereunto were you called: because Christ also suffered for us, leaving us an example, that you should follow his steps.