Yes, traders should choose a single currency pair for trading on which he or she will gain much more knowledge. When a trader trade in multiple pairs, it becomes hard for him to gather expertise on all of those pairs altogether.

Price info indicator needed - one pair's price x another pair 5 replies
Multi-pair trading or Few-Pair Trading. [poll] 15 replies
Choosing the base currency 7 replies
currency over a currency pair 1 reply
choosing a broker 2 replies