As per PMBOK Guide, there are 3 core competencies which PM Should have and those are

1.Technical knowledge, 2 Leadership & 3. Strategic & business management

The estimation and risk management aspects of project comes under the technical knowledge management areas of project management such as resource/cost/activity estimation and risk management.

In Practice, the PM are found frequently rely on the expert judgement for both estimation purpose and risk management.

Lets understand from an example of estimate - suppose there is a project to develop suite of test cases for testing a web site using a tool called Selenium.

Now, the best resource to "estimate" how much time will be required to complete such suite could be a technical test architect who has previously worked on a tool such as Selenium & "knows" how much time each test case takes to develop using this tool.

The PM himself might never has used this tool and hence he cannot say for sure how much time it will take to develop the test suite & in such case PM has to rely on this technical expert's judgement as far as estimation is concerned.

So essentially, apart from being aware of personal expertise, PM must know to find others with the needed expertise, to be successful as project manager.

As per PMBOK Guide, there are 3 core competencies which PM Should have and those are

1.Technical knowledge, 2 Leadership & 3. Strategic & business management

The estimation and risk management aspects of project comes under the technical knowledge management areas of project management such as resource/cost/activity estimation and risk management.

In Practice, the PM are found frequently rely on the expert judgement for both estimation purpose and risk management.

Lets understand from an example of estimate - suppose there is a project to develop suite of test cases for testing a web site using a tool called Selenium.

Now, the best resource to "estimate" how much time will be required to complete such suite could be a technical test architect who has previously worked on a tool such as Selenium & "knows" how much time each test case takes to develop using this tool.

The PM himself might never has used this tool and hence he cannot say for sure how much time it will take to develop the test suite & in such case PM has to rely on this technical expert's judgement as far as estimation is concerned.

However, what PM Must know regarding the estimate is below key points,

1. how it was developed
2. explain/document all the assumptions made while estimating
3. list down any known constraints
4. indicate the confidence level of the estimates

So essentially, apart from being aware of personal expertise, PM must know to find others with the needed expertise, to be successful as project manager.