The purpose of your visit is not your itinerary, but the reason you want to come to Canada.
Basically, for visitor visas (tourism or business visas, mostly), they want to be sure you come for the purpose stated (tourism or business), not for other reasons (to enter Canada to then stay, live and work there — there are other visas for that, with other conditions — or even worse, to stay and live in Canada and then rely on public funds or illegal activities).
There are quite a few factors which they can take into account to determine this:
- Statistics on previous visitors: if visitors from a given country are more likely to overstay, there will be a higher scrutiny for other applicants for the same country.
- Whether the cost of your trip is proportionate to your revenue and/or wealth: if you earn 100 dollars a month and plan a trip costing $1000 for holidays, they are very likely to find that very suspicious.
- Your economic situation at home: if you have no job or a job that, by Canadian standards, pays very little, you have a strong incentive to try to stay in Canada and earn a living even covertly.
- Any ties you may have in Canada: if you have a partner, family or other relatives in Canada it makes it more likely you will try to overstay.
- Discrepancies between your statements and reality: if you state you are going to spend $5 per day for lodging and food in Canada as a tourist, they are not going to believe it.
- And many many more reasons.
Some cases are quite obvious and call no discussion. In many other cases, it’s the overall balance of points for and against which will result in the decision.
You haven’t told us anything about your application (the stated purpose, duration, cost, whether you have a sponsor, who they are, your citizenship, your current situation, your travel history, the documentation you provided…), or any details of the refusal, so we can’t tell you more. It might be a simple error which can be easily addressed, or it could be a fundamental issue in your situation or application which makes it extremely unlikely you will ever get that visa unless your situation changes dramatically.
But remember, a visa is not a right. It’s like applying for a job or for a top university: you have to convince them that letting you in is good for them.
The factor which probably has the biggest importance is your economic situation. People with a stable well-paid job (by Canadian standards) are a lot less likely to undergo a higher level of scrutiny.