If one wishes to add on more restrictions than the law requires, one may do so for oneself, but not [make such demands] of others (Shulchan Aruch).
Some people employ a double standard. One set of rules applies to themselves, and another to everyone else. The Shulchan Aruch, the standard authoritative compilation of Jewish law, accepts this policy - but on one condition: the more restrictive set of rules must apply to oneself, and the more lenient apply to other people.
Guidelines exist for many things, such as the percentage of income that one should give for tzedakah. Many tzaddikim, righteous people, retained only the barest minimum of their income for themselves, just enough to provide for their families, and gave everything else to the poor. However, they would never expect anyone else to follow their example, and some even forbade it.
Our minds are ingenious in concocting self-serving rationalizations. Sometimes we may have excellent reasons not to give more liberally to tzedakah, even if it is within the required amount. We may project into the future, worry about our economic security, and conclude that we should put more money away for a rainy day. Yet we often criticize people who we feel do not give enough to tzedakah.
We should be aware of such rationalizations and remember that the more demanding rules should apply to ourselves. If we are going to rationalize, let us rationalize in a way that gives the benefit of doubt to others.