The Dunning-Kruger Effect
The Dunning-Kruger Effect on Wikipedia
If you're incompetent, you can't know you're incompetent... The skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is.
The Dunning–Kruger effect is a theoretical cognitive bias which was described by David Dunning and Justin Kruger in a 1999 psychological study and paper. The study suggests that people with a low level of ability at a task are likely to overestimate their ability of the task. The proposed reason for this bias is that a sufficient awareness of the complexity of a problem or domain is required for a person to be able to make an informed opinion of their capability to work in that domain.
The Dunning-Kruger effect has sometimes been used to describe a related, but not necessarily implied effect which could be described as "The less a person understands a domain, the more they are likely to believe they can easily solve problems in that domain, as they are more likely to see the domain as simple". This more general effect is highly relevant in technology. It would suggest that people who are less familiar with a domain, such as non-technical team members or less experienced team members, are more likely to underestimate the effort required to solve a problem in this space.
As a person's understanding and experience in a domain grows, they may well encounter another effect, which is that they tend to overestimate the ability of others or underestimate their own ability, as they are have become so experienced in the domain. In all cases these effects are cognitive biases. As with any bias, an understanding that it may be present will often be sufficient to help avoid the challenges — as when there is awareness of a bias, more inputs and opinions can be included to attempt to eliminate these biases. A closely related bias is that of Illusory superiority.
Real-world examples: