Flavour, aroma and colour (of the infused tea) are the essential qualities looked at when the quality of teas are assessed.
Consistency, which expert tea blenders try to achieve, is not easily or always obtained.
Tea is a natural agricultural product and seasonal factors can and do, affect the flavour (very similar to wine).
Tea packed at different months of the year will vary in flavour.
Tea producers often wish it can be artificially manufactured to a formula – that would make life so much easier! But then it will be so boring!
Water, location and changes in medication can affect the flavour of tea as well. Storage in an airtight container is also a must.
Additionally one can become slightly desensitised to the flavour by regular use.
For example, visitors to a tea warehouse will often remark on the beautiful aroma of tea when they enter the premises.
Sadly, the people who work daily in that environment cannot enjoy it – they are totally desensitised!
However, if they are away for a week or so they can actually experience the aroma when they return!
A suggestion (if you are experiencing a variation of flavour in the teabag is that you use) is that you try brewing leaf tea (actually cheaper by the cup) rather than tea bags.
This will enable you to vary the quantity used, to give you the brew you desire.
But remember, although brewed tea will usually give you a better tea experience and that all teabags are not bad, you must use GOOD QUALITY TEA AND TEABAGS and not the generally cheap and nasty varieties found in major supermarkets.