It's a bit of a cliché nowadays to say that what you think determines what happens, but what you think about certainly controls what you do. And if you wonder why nothing ever seems to go right, then maybe you're unconsciously rehearsing how to make things go wrong.

If I say to you "DO NOT think about a purple elephant!", what immediately happens? You really can't help yourself thinking about a purple elephant, even if you've never seen one and have to imagine what it looks like (or sounds like or feels like).

It's as though the brain edits out the "not" and the instruction becomes, "Do think about..."

So what does it matter if you think about something you're trying not to? Well, perhaps you're trying to avoid thinking about making a mistake. Did your mother ever warn you to take care not to spill the drink you were carrying? By mentioning "spilling", she makes sure that you now picture yourself doing just that. And maybe you started wobbling and... the inevitable happened.

The lesson here for parents instructing their children is to be clear about what you're asking them to do rather than warning them not to do something. But the principle applies to all ages and situations.

That's not to say that people will be unable to resist going through a door labelled "Do Not Enter" - although they might imagine doing it. But it will be more difficult for them to achieve a complex goal if it's put to them as a negative statement. "Don't miss the sales target" fills the mind with pictures, sounds and emotions of failure that reduce resourcefulness.

There are signs on the A1 in Northumberland warning drivers, "Don't Speed!". Whatever effect this has on driving behaviour, for me it always conjures up the picture of wild-eyed Mr Toad, behind the wheel, careering through the country lanes in The Wind in the Willows. Perhaps it would be more useful to design signs that evoke images of traffic moving steadily and safely along.

Sometimes this automatic deletion of "not" can be useful. In coaching, when you want someone to focus on a particular issue that they're apprehensive about or a problem that they doubt their ability to solve, you use the formula, "In a minute, but not yet, you're going to...". Despite the "not yet" part, they immediately start to think about the problem, but it feels like they're only practising - it's not the real thing - so the usual inhibitions are lifted.

It has a similar effect to the "soft framing" of those questions that requires creative answers. "What are some of the ways you could...?" encourages experimentation whereas "What will you do?" carries the implication that you only have one chance to get it right.

There's a construction called the "Well-Formed Outcome" that's analogous to SMART objectives, but with nine components rather than five. The very first part of it is to state what it is that you positively want, as opposed to what you want to get rid of. If you think about what you don't want then you unconsciously fix it in place.

Perhaps you always focus on what you want to achieve or gain. Or maybe you're more often driven by the need to avoid or get rid of something. If the latter, then you're bound to spend a lot of effort constantly reminding yourself how bad it all is, which leaves less effort to plan how to move forward.

The more often you think about the feared thing, imagining what will happen if you meet it face to face, the deeper the mental groove you wear. And of course, if you imagine a positive, successful encounter then that's what your unconscious begins to expect and to prepare for.

Like almost everything discussed in these articles, it's a matter of habit. When you have to give instructions, at work or at home, take the time to frame a positive statement of what you want done. Leave people thinking about how to do it rather then what to avoid doing. And tune in to your internal dialogue to catch the negative language you use on yourself - then deliberately change it. At first it will seem artificial and almost self-deceiving, but soon it will become part of your vast set of unconscious patterns.

Want to know how? Don't even think about it!