There are times when I think that -- yay! -- I've got this. I'm chatting away fluently and the words are coming easily and everything is going great, and then I try to explain something a little more complicated and come to a stumbling halt as I realise that I've headed into a conversational boggy bit where I just don't have the vocabulary.
It's like walking briskly along a well-defined path and then deciding to venture off down a side path, only to end up tangled in brambles and ankle deep in mud. I have to do a mental halt, regroup the thoughts and try to find a way around. At least with Welsh you can always throw in the English word or phrase and keep going, which you wouldn't be able to do with native speakers of other languages.
And in other news, to change the subject completely, I managed to exchange the packet of ham I bought on Monday. It was only when I got home and was deciding what to have for lunch that I realised that the Use By date was 7th November and I'd bought it on the 11th. I took it back to the Co-op and they exchanged it without any problem. So that was a Useful Thing done today.