London is a big, bewildering place and often feels like one long winding road. For newcomers, the prospect of knowing London can be discouraging. There's so much to see and do in this city that it seems impossible for visitors to get anywhere with just a single visit! I've been here over thirty years myself now - there are still new things happening nearly every day as well.
The city is a living, breathing entity. If you rush around visiting all the tourist sites in one day without experiencing it as an everyday citizen then I guarantee that you will be frustrated.