Saying "yes" to a client or fellow professional is both positive and non-confrontational. However, failing to deliver on your “yes” usually results in significant headaches further down the line.
"Yes" is an appropriate response to a request that can be achieved even in the most adverse circumstances - usually for relatively routine, less challenging requests and ones that can be easily delegated.
"No" means "No". Usually it means closing a door. Some doors should be closed, others kept slightly ajar, and some left open. That’s why a conditional yes is often preferable to an unconditional “no”.
Deadlines
As engineers we are in the middle of the design process (sandwiched between the architect and the builder) and often under pressure to reduce timelines for the delivery of our services - in order to account for delays caused elsewhere.
Saying "yes" to a difficult deadline is the easy option in the moment, but in retrospect an inability to say "no" will ultimately diminish trust with your clients and others because, when you fail to deliver, they will either not wish to engage with you in future, or do so on less trusting terms. Either outcome has reduced not enhanced your position.
Perhaps it is better to always use a qualified "yes" and "no" - one with strings attached. "Yes, subject to receiving the architects' revised drawings by close tomorrow" or "no, unless we can increase our fee to allow for overtime working”.
Sub-standard work
On occasions, engineers are belatedly asked to confirm that sub-standard work is OK. Perhaps the builder has deviated from the drawings, or worked to out of date information, or simply gone off-piste whilst doing the build.
The answer must be "no". You should never bow to such pressure, as doing so makes you responsible for others’ failures and introduces risk to your and other members’ reputations.
Early career pressure
While you’re climbing the career ladder, or in the early stages of building your own business, it is more tempting to want to say "yes". But it is still only the correct answer if given for good reasons. Agreeing to do something that is not sound usually has negative ramifications in the long term – for your career and for your business.
Turning down work
The cyclic nature of our industry means that sometimes we find ourselves inundated with offers to engage in quality projects, to the extent that we have to turn some of the work away.
Hindsight is a wonderful gift, and I can assure you that it is better to say "no" and not accept a project, than to spend prolonged periods answering the phone and explaining why work has not been completed by the agreed dates.
Ideally, the answer "no, unless we can defer delivery of design by two months" or such like, is a better response - because it still retains the opportunity to retain the work, and it also avoids the finality of a "no".
A Spanish friend recently told me not to say "Adios", because it can mean "I will not see you again", they advised "Hasta Luego" (see you soon).
Any device that retains clients is usually beneficial as it takes time to establish working relationships and a rapid turnover of clients needs to be avoided. So "no" must be used wisely.
If in doubt, look to the Code of Conduct
IStructE members should be aware that some employers are employing the qualification, and not the person. In such circumstances the IStructE Code of Conduct can give you support in saying "no", although it will still be a career decision that you are making.
Employers
I believe it is better not to intervene in employees’ decision-making: better to support them, allowing them to make decisions, and clearly define decision making powers for employees according to their experience.