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Well let me cite an example. Say you are a trader and you ender a trade and then you are mid way between the completion of the trend according to your prediction and analysis and then you spot an invalidation of your analysis which suggests the opposite trend sooner. If you should still stay in such trade without at least securing your profit then that's greed. However staying in a trend and bearing a retest without any invalidation can be viewed as RISK.
Well sometimes in such situations, there could be certain exceptions, if the trader in question has only wagered or traded with an amount he's willing to lose, and is actually willing to accept the losses in good fate then I wouldn't really consider seeing the trade to the end as being greedy. This is because, after a trade, a trader either of two things or even both, which is profits and experience, the profits may not always come, but at the end of trade, a trader may have one or two lessons to take home, which when applied on the next trade could have better results.
Additionally, most traders in the same situations who ended up taking their profits, ended up regretting at last as their market later went according to their predictions, so sometimes indication of an opposite trend may not always be accurate as the chances of the trade going the opposite direction could be slim. So if the trader can actually afford to lose whatever amount he wagered, then surely i feel the risk is worth taking.