Why do Managers/Team Leads judgement on people goes wrong

Many a times managers misjudge the people working under them .Managers are also humans who go as per there nature .Each one will have there own expectations .Some managers see the actual stuff of a person and some see if the person has reached the expectation kept my them. But ever the nature of the manager is , assuming he sticks to it , then he should be able to judge his total team in the same way.But here are some reasons why this wont happen and one team mate is rated above other.

Let us consider 2 people who work under a lead . Both of them are equally talented and both of them work hard.

Reason 1: One of them is a smart ass who informs everything to the manager , even the smaller things like a dog eats biscuit .The other person is cool person who solves all the problems which he gets by himself and wont say to the manager the smaller things .But here the first one gets a good appraisal. Here the manager is blindfolded by the stupid smartness of the first guy and he is actually a bad manager

Reason 2: The one who talks more to the lead is the good guy and the other is the bad guy.So being non-talkative is a bad virtue of the poor second guy who always remain second

Reason 3: Third reason is not being a show off . The first guy sends reports to the team all the time .I say sending a report means the report can have any thing. The report can be a manipulated one , half baked one or even can be a total failure report .But where as the second guy who works hard to get the work done correctly is the bad guy.As he took a bit of extra time to send a report , he is the bad guy.

Reason 4 : Very few managers do cast there vote based on the region/caste basis although this percentage is very less. These sort of managers could just be shot out of sight.

Reason5 : The final one is the tough one. Each person is allocated some work by the manager. Let us assume 2 persons are given some x and y works which can be rated of the same level. Person 1 does work x with full concentration , this guy digs his work really well and does it perfectly . On the other hand person 2 does work y to some extent and he also sees work z which was not allocated to him , but has some value . Output wise , the amount of benefit the company would have got will be same . Now comes the appraisal time when a manager have to calculate the appraisal .Many managers do things wrongly here . Some managers feel the work a person1 as bigger and rate him above the other , where as some managers feel that the person2 is taking care of other works too and his doing good work . But this is totally wrong . Both the persons should be rated same here .

Note : Words Manager and Lead are both used here . Replace them as per ur convenience who ever gives an appraisal for you.