Design bugs are often subtle and occur by evolution with early assumptions being forgotten as new features or uses are added to systems.

One is faced with a dilemma: If one places total trust in all other users, one is vulnerable to the antisocial behavior of any malicious user consider the case of viruses. But if one tries to be totally reclusive and isolated, one is not only bored, but one's information universe will cease to grow and be enhanced by interaction with others. The result is that most of us operate in a complicated trade-off zone with various arrangements of trust and security mechanisms.

The general problem with ambitious systems is complexity. [...] it is important to emphasize the value of simplicity and elegance, for complexity has a way of compounding difficulties.

My definition of elegance is the achievement of a given functionality with a minimum of mechanism and a maximum of clarity.

The number of lines of code a programmer can write in a fixed period of time is the same independent of the language used.

Regardless of whether one is dealing with assembly language or compiler language, the number of debugged lines of source code per day is about the same!

Because one has to be an optimist to begin an ambitious project, it is not surprising that underestimation of completion time is the norm.