3 types of work - yesterday, today and tomorrow

I found it is useful to describe software developer's daily job into 3 different types: yesterday, today and tomorrow.
Yesterday: bug fix, maintenance job. since this kind of job is based on the product which is supposed to be finished, so I describe it as yesterday.
Today: developing phase, the work on the product is under development,
Tomorrow: some research and R&D work.
These 3 different type has different nature, and they need different mindset and strategy to deal with them.
Let me dig them into deeper.

Yesterday's work
Yesterday's work are bug fixing and maintenance job. This kind of job is putting off fire, they are urgent, and undeniable. We need to fix them ASAP.

Yesterday's work has no value or negative value, because customer already paid us up front, this work is support and service. This kind of job is not adding value, but removing the negative value.
The more time and effort we spend on the yesterday's work, the less value remained for us. The cost of fixing a bug in production phase is much expensive than fixing it in developing phase( today's work).

Yesterday's work is quite stressful. A minor issue delayed in yesterday will cause higher priority work. Yesterday's job is quite critical for time. we just need the job get done, there is no time for refactoring, no time to focus on better design. There is no room for developer to improve the system (code base, design, code quality etc) at this stage.

If there are too many yesterday's work, then this is not a good signal: It means we have a large amount of technical debts from today's work, it means bad design and careless decision.
So yesterday's job is highly dependent on today's work.
Ideally we should keep the number of yesterday's work as low as possible.

Today's work
Today's work is about current realistic issues. Today's work is the tasks which is belong to developing phase. We develop a new feature which is our customer wanted, so this job will bring values. They are urgent and important, but some features can be negotiable. Customer will focus on feature than time, so the time is not so critical as Yesterday's work.
Developer has lots of room to improve the system, he can have time to improve the design, refactoring.

The strategy of today's work will be - Build quality in. Focus on quality over time. If we focus on quality at this phase, then time must be shorten on maintain phase.
Quality means more than functionality, also means maintainability and readability.  We should focus on simple design, write clean code, keep refactoring. and do not easily leak the bug to maintenance phase.

Tomorrow's work
Tomorrow's work is focused on research and innovation. It will bring us potential value in future, so I call it tomorrow's work, means work for tomorrow.

It for a long term goal, we might not realize its value at present. it's important but not so urgent.

Tomorrow's job is like investment. there is a risk, we don't know how much value it will bring us.

Usually the priority of tomorrow's work is less than yesterday and today, if there are too many work spending on yesterday and today, then there is no time for us on investment. But if we did a good job on today's work, then we need less time on yesterday, then we have more time spending on tomorrow.

Mapping to First thing first
I found these 3 types of work map perfectly with Stephen Covey's first thing first :
Yesterday - Urgent but not important
today - Urgent and important
tomorrow - Not urgent but important

Conclusion
Yesterday is your debt, today is your earning, tomorrow is your investment.
We need to focus on today's work, keep improving the quality of today's work.
If we want to be productive, we need to balance these 3 types of work wisely.