There is a certain type of person who completes law school and actually practices law. Some get to law school, see what it is and leave. Others get the degree but go into business or other non-law practice pursuits. Those who follow through are people who like (probably "love" or "need" are more accurate terms) to win. More importantly, we HATE to lose. The joy of victory is surpassed only by the agony of defeat.
We expect to win by force of our own ability to persuade. We are surprised when a judge does not agree with our reasoning.
We expect to win even when our client is caught lying. We expect to win even with the facts or the law against us, and even though we have fully advised the client of this and that the odds are against us.
Is this personal investment in every case a good thing or a bad thing? It is definitely bad when it leads lawyers to ignore the reality of the case or the client. You may take it personally but you cannot let that interfere with doing the job properly. You cannot turn the client's case into a personal vendetta. You also need to tell the client in a brutally honest way what the flaws are in the case and to tell them when it is futile to continue. It is a good thing because lawyers work incredibly hard for their clients. They give each case their complete effort. A good lawyer does not have "small cases". All cases are important.
There is great frustration when the client does not provide all-or accurate-information. This is magnified when a client lies in court. The lawyer and the client are a team. Even when the crucial player on the team (the client) fails to perform, we still expect to win.