My cactus is dying. =(

For those who don't know, I bought a cactus last year and placed in on my office table. I was going to water it last Thursday when I realised that one side of it, near the roots, had turned black.

I started to panic. My colleague told me that it could be because I've over-watered it. I supposed this has been going on for quite a while, since it would not have turn black overnight. If only I had noticed the symptoms earlier, except that I don't know what to look out for in the first place. Until it's too late.

Perhaps at times, life is like that too. We don't notice the symptoms til it's too late.