As with most things - it depends.

You can get lousy consultants and great consultants. You can also get naïve or stupid clients, and informed and focussed clients.

Good clients can make a mediocre consultant look good while lousy clients can thwart even the best consultant.

The experienced consultant (strategy or not) will be able to:

1. 'Read' the client's seriousness and competence quickly - certainly before he/she commits or even scopes the project.
2. Read the client's culture.
3. Explore the client's change history and readiness.
4. Explore the client's experience and behaviour with consultants.
5. Establish whether what's needed in the consultant's experience sits within the client's expectation for the task they're asking the consultant to deliver.
6. Determine whether the robustness of the relationship between the 'objective' of the initiative and the work effort required to deliver it is clear and compelling (i.e. that the 'cause and effect' are indisputable.)

I have found that strategists that become too familiar with a client's environment tend to think like the client. If that were not so, then all the problems in industries in which strategists work would have been resolved - and that is certainly not the case.

I have also found that coming into a problem with 'new eyes' (and ears) allows lateral solutions to be introduced - and  real value delivered.